Definition 2.7 (\(\alpha \) -divergence [1]})
Let \(\alpha \)  be a real parameter.
The \(\alpha \) -divergence between two probability vectors \(\mathbf {p}\)  and \(\mathbf {q}\)  is defined as
\(D_\alpha [\mathbf {p}\Vert  \mathbf {q}] = \frac{4}{1-\alpha ^2}\Big (1 - \sum _i p_i^{\frac{1-\alpha }{2}}q_i^{\frac{1+\alpha }{2}}\Big ).\) 

